..: A brief history of the 446 MHz band

In 2001, the PMR446 band was created as a replacement for the now-defunct RPS band, which consisted of 3 frequencies (446.9500, 446.9750, and 446.9875 MHz).

Since June 2018, the PMR446 band has comprised 16 analog channels spread across the 446.0 to 446.2 MHz range.
For more information, visit this specialized website on analog PMR446.

In 2005, ETSI* developed a new standard called Digital Mobile Radio (DMR), which was less bandwidth-intensive. It was primarily intended for professionals such as taxis, ambulances, municipal services, etc., operating on licensed PMR bands. In addition to voice communication, DMR allows the transmission of data such as SMS, GPS coordinates, real-time information, etc.

Since 2018, we have a single radio band ranging from 446.0 to 446.2 MHz, accommodating 16 license-free analog and digital channels. The choice is up to the user.

..: What is DMR?

DMR (Digital Mobile Radio) is the name given to the set of digital voice and data transmission methods available on professional VHF/UHF bands. These methods have been designed and implemented by ETSI*. They allow the simultaneous transmission of voice and data on a single frequency.

DMR comes in several versions, called Tier, which offer a range of options based on the needs of the end user.

DMR Tier I
The simplest tier, it uses FDMA (Frequency Division Multiple Access) for voice and data transmission by dividing the channel into two separate parts (a 12.5 kHz channel split into two narrower 6.25 kHz channels). It operates without license. The maximum allowed radiated power output is limited to 500mW, and the antennas must be integral to the handheld radios. This tier encompasses all communications in the digital PMR446 band (dPMR446 and DMR446) and must comply with the technical specifications of the ETSI-TS-102-490 directive.

DMR Tier II
This tier is only authorized on licensed frequencies because it operates using TDMA (Time Division Multiple Access), which is a voice and data multiplexing technique that divides the transmission time into two parts. The creation of repeaters is possible. We will discuss TDMA in the following paragraph as it is of significant interest.

DMR Tier III /// Will not be covered on this website
It is used similarly to Tier II but allows the use of multiple frequencies ranging from 60 to 900 MHz. It supports the transmission of complex SMS messages and allows for the creation of repeaters and the use of IP4 and IP6 relay systems.

..: What is DMR446, then?

DMR446 is the combination of the quality of digital voice transmissions with the free and license-free PMR446 band.
As mentioned earlier, only digital Tier I is authorized on the PMR446 band using FDMA. To comply with this requirement, manufacturers have adapted to the directive by creating handheld radios capable of supporting digital voice or data transmission on a smaller bandwidth (6.25 kHz instead of 12.5 kHz) through the use of efficient codecs (AMBE+2).

The first preprogrammed FDMA handheld radios appeared around 2007 and featured 16 channels distributed within the famous band ranging from 446.103125 to 446.196875 MHz.

Currently, these radios are still in use, as shown in the table below:

The devices were expensive and often incompatible with each other. Each manufacturer developed its own codec or made slight modifications to AMBE+2, aiming to create an essential standard that would force users to buy all models within their network and not from competitors. As a result, no standard truly stood out, and digital dPMR446 never gained significant popularity.

HYTERA, a manufacturer with a strong presence in the professional DMR Tier II market, took advantage of its unique digital production line and sought to tap into the potential lucrative consumer digital market. They devised an alternative solution to bypass the European directive that mandated FDMA transmissions.

Indeed, the supplier of portable and mobile products, deeply rooted in the professional DMR Tier II market, envisioned manufacturing the first license-free digital handheld radios (PD365LF, PD505LF, and PD355LF) using the "prohibited" technology on the PMR446 frequencies (as it belonged to Tier II).

To achieve this, and to avoid setting up a special production line for dPMR (i.e., FDMA), HYTERA adapted the TDMA technology by utilizing the capability to transmit on both time slots simultaneously (PSEUDO-TRUNK mode).
Thus, the problem was solved. The entire bandwidth (12.5 kHz) was utilized across both communication slots (see the diagram on the right).

Above is a sketch that illustrates the differences between analog, FDMA, and TDMA.

Diagram showing TDMA as it should be on authorized frequencies and TDMA as proposed by HYTERA to operate on the PMR446 Digital band (446.1 to 446.2 MHz)

Therefore, a license-free Hytera DMR446 handheld radio (or equivalent from the cheap Asian market) should be programmed with 16 channels, as shown in the table below, to comply with the European directive on digital transmissions in PMR446.

Any other handheld radio programmed with slot alternation, and therefore with 16 channels, will work fine but will not comply with the PMR446 digital standard.

..: Does DMR446 work better than PMR446?

Undoubtedly, DMR brings significant improvements for the user.

Example:

Sending pre-programmed or written text messages (depending on the handheld device)

In the diagram below, you can observe that the sound quality of the communication is optimal and consistent throughout the entire duration, regardless of the distance, up to the ultimate limit of the transmitter's range.
With an analog handheld radio, the sound quality would have declined gradually to the point of being completely inaudible, even if there was still some reception signal remaining.

Watch this video example to appreciate the radio quality:

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